Regulated and unregulated emissions from a compression ignition engine under low temperature combustion fuelled with gasoline and n-butanol/gasoline blends

• The regulated and unregulated emissions of n-butanol/gasoline blends were studied.
• n-Butanol/gasoline blends offer superior regulated emission benefits than gasoline.
• NO and NO2 proportions are influenced by the local equivalence ratio actually.
• HCHO has a good linear correlation with total exhaust HC.
• The formation of aldehydes compounds is improved by the addition of n-butanol.

In this paper, the study on the combined effects of EGR and n-butanol additive on the regulated and unregulated emissions from a CI engine has been conducted at a load of 0.9 MPa IMEP with the speed of 1500 rpm. Mixtures of 0%, 10%, 20% and 30% by mass fraction of n-butanol with gasoline fuel were evaluated, referred as B0, B10, B20 and B30. The results show that n-butanol additive can effectively reduce soot emissions, while the EGR rate that corresponds to the peak value of soot is also decreased. With lower EGR, CO and HC emissions are low and not affected by fuel properties; in the LTC region with higher EGR, n-butanol additive improves the oxidation of CO and HC emissions slightly, whereas still has little impact on NOX emissions. In the unregulated emission respects, NO proportion in total NOX decreases while NO2 shows an opposite trend as EGR increases, and NO2 proportion reaches up to 25% with EGR of 45%. n-Butanol additive has almost no effect on the proportions of NO and NO2, which indicates that the local equivalence ratio plays a more important role in influencing NO and NO2 proportions compared with the global oxygen concentration. Under LTC condition, the primary individual hydrocarbons include C2H4, C3H6, NC5, IC5 and AHC, and their proportions in total HC increase with higher n-butanol fractions except AHC’s. CH4 has not been a major issue yet in Gasoline LTC due to less EGR used, while AHC proportions decrease with the increase of n-butanol fraction. HCHO has a good linear correlation with total exhaust HC, and the ratio of MeCHO to total HC exhibits decrease first and then increase with the increasing EGR, while the formation of both HCHO and MeCHO is promoted by the addition of n-butanol in the blends.